A biomass boiler ammonia injection amount feedforward control method based on LIBS identification

Abstract

The application discloses a biomass boiler ammonia injection amount feedforward control method based on LIBS identification, which comprises the following steps: performing field test, changing fuel source, recording N element content in fuel, monitoring furnace combustion temperature and inlet NOx concentration, and obtaining fitting curve; during fuel feeding, on-line detection is performed on the N element content in the fuel and the N element content is uploaded to a control center in real time; during fuel incineration, on-line monitoring is performed on the furnace combustion temperature and the furnace combustion temperature is uploaded to the control center in real time; a predicted value of the inlet NOx concentration is calculated; calculated flue gas flow is obtained; a feedforward correction amount of the ammonia injection amount is calculated, and the feedforward correction amount is applied to an ammonia injection system to control the ammonia injection amount to change in advance. The application realizes element content analysis based on LIBS, can predict the inlet NOx concentration, calibrate the measured flue gas flow, calculate the feedforward correction amount of the ammonia injection amount, control the denitration device to give a signal in advance, and solves the problems of inaccurate measurement and feedback lag.

Description

Technical Field

[0001] This invention belongs to the field of flue gas denitrification technology, specifically relating to a feedforward control method for ammonia injection in a biomass boiler based on LIBS identification. Background Technology

[0002] Biomass, as a zero-carbon emission fuel, is primarily utilized through direct combustion. However, with increasingly stringent emission standards for biomass boilers, NOx emission requirements are also becoming more stringent. Due to significant differences between biomass boilers and coal-fired boilers in terms of fuel, combustion and NOx emissions also differ considerably. However, current denitrification technologies for biomass boilers are largely consistent with those for coal-fired power plants. This leads to a series of problems, including large fluctuations in fuel quality, combustion performance, initial NOx concentration, and difficulty in controlling NOx emission concentrations. These issues frequently result in excessive NOx emissions or over-injection of reducing agents. Furthermore, high ash and chlorine levels can cause coking and corrosion problems. Summary of the Invention

[0003] To address the technical problems existing in the prior art, the purpose of this invention is to provide a feedforward control method for ammonia injection in biomass boilers based on LIBS identification.

[0004] To achieve the above objectives and technical effects, the technical solution adopted by this invention is as follows:

[0005] A feedforward control method for ammonia injection in a biomass boiler based on LIBS identification includes the following steps:

[0006] First, a field test was conducted. During the test, the fuel source was changed, the nitrogen content in the fuel was recorded, and the furnace combustion temperature and inlet NOx concentration were monitored. Based on the nitrogen content, furnace combustion temperature and inlet NOx concentration, a fitting curve was obtained and stored in the database for later retrieval.

[0007] During the fuel feeding process, the nitrogen content in the fuel is detected online and uploaded to the control center in real time; when the fuel is burned in the furnace, the combustion temperature in the furnace is monitored online and uploaded to the control center in real time.

[0008] Based on the detected temperature and N content data in the fuel, and combined with the fitted curves in the database, the control center calculates the predicted value of the inlet NOx concentration.

[0009] Obtain the calculated flue gas volume;

[0010] Obtain the corrected ammonia injection rate and apply it to the ammonia injection system to control the ammonia injection rate to change in advance.

[0011] Furthermore, the expression for the fitted curve is:

[0012] CNOx,in =f(N) in ,T)

[0013] Among them, C NOx,in NOx concentration at the inlet; N in The nitrogen content is denoted by N; T is the furnace combustion temperature.

[0014] Furthermore, the nitrogen content in the fuel is detected online using a LIBS testing instrument.

[0015] Furthermore, the steps for obtaining and calculating the flue gas volume include:

[0016] In addition to detecting the nitrogen (N) content in fuel, the LIBS analyzer also detects the C, H, O, and S content, combining the readings of O2 and CO with those of T, P, RH, and Q. 燃料 The measured value is used to calculate the theoretical flue gas volume Q. 理论烟气 Theoretical flue gas volume Q 理论烟气 This will affect the measured flue gas volume Q 实测烟气 After correction, the calculated flue gas volume Q is obtained. 计算烟气 The calculation formula is:

[0017]

[0018] Furthermore, the formula for calculating the corrected ammonia injection amount is as follows:

[0019] Q NH3修正量 =Q 计算烟气 ×(C NOx,in,预测 -C NOx,in,实测 )÷46×17÷1000000

[0020] In the formula, Q NH3修正量 To correct the ammonia injection rate, C NOx,in,预测 C is the predicted value of the inlet NOx concentration. NOx,in,实测 This represents the measured value of the NOx concentration at the inlet.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] This invention discloses a feedforward control method for ammonia injection in a biomass boiler based on LIBS identification, comprising the following steps: First, a field test is conducted, during which the fuel source is changed, the nitrogen (N) content in the fuel is recorded, the furnace combustion temperature and the inlet NOx concentration are monitored, and a fitting curve between the N content, furnace combustion temperature, and inlet NOx concentration is obtained and stored in a database for later retrieval; during fuel feeding, the N content in the fuel is detected online and uploaded to the control center in real time; during fuel combustion, the furnace combustion temperature is monitored online and uploaded to the control center in real time; based on the detected temperature and N content data in the fuel, combined with the fitting curve in the database, the control center predicts the NOx generation concentration; and the theoretical flue gas volume Q is calculated. 理论烟气 This invention uses LIBS to correct the measured flue gas volume to obtain the calculated flue gas volume; it also calculates the feedforward correction for ammonia injection and applies it to the ammonia injection system to control the ammonia injection volume to change in advance. Based on LIBS, this invention analyzes the content of multiple elements (C / H / O / N / S), combines it with measuring instruments such as temperature sensors to predict the inlet NOx concentration, calibrates the measured flue gas flow rate, and finally calculates the corrected ammonia injection volume or the ammonia injection feedforward correction. This controls the denitrification device to give an advance signal, controlling the ammonia injection volume to change in advance. This allows for precise control of denitrification even under the characteristics of large variations in fuel and combustion in biomass boilers, preventing excessive ammonia escape or excessive nitrogen oxides in the chimney, and solving the problems of inaccurate measurement and delayed feedback. Attached Figure Description

[0023] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0024] The present invention will now be described in detail so that its advantages and features can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0025] The following provides a brief overview of one or more aspects to offer a basic understanding of them. This overview is not an exhaustive summary of all conceived aspects, nor is it intended to identify key or decisive elements of all aspects, nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form to prepare for the more detailed descriptions that follow.

[0026] Definitions:

[0027] LIBS stands for Laser-Induced Breakdown Spectroscopy.

[0028] Ammonia injection rate Q at biomass power plant NH3 The calculation formula is:

[0029]

[0030] The main parameters involved in the above formula are flue gas flow rate Q. 烟气 Denitrification efficiency η, inlet NOx concentration C NOx,in NOx concentration at export, ammonia slip concentration C NH3 Currently, these parameters are all measured values ​​from the dial indicator, but there are two problems: one is a certain lag, meaning that the measurement results are fed back to the denitrification control system, and the control system then issues feedback to control the ammonia injection valve, resulting in a delay; the other problem is insufficient measurement accuracy, especially for flue gas flow measurement. This invention addresses these two problems by using a LIBS identification method to predict NOx formation concentration and provide control signals in advance, thus solving the problem of lag feedback and significantly improving measurement accuracy.

[0031] NOx produced after fuel combustion mainly originates from fuel-based, thermal, and rapid sources. Fuel-based NOx is generated during the combustion of nitrogen (N) in the fuel; thermal NOx is generated from N2 in the air under high-temperature conditions; and rapid NOx is generated by the reaction of CH radicals (CH2 free radicals) produced by the high-temperature decomposition of carbon oxides with nitrogen in the air. With a constant N content, the amount of fuel-based NOx generated is higher, while the production of thermal NOx is directly related to the combustion temperature in the furnace. For biomass boilers, NOx is mainly of fuel-based and thermal origin, with the former accounting for approximately 95% and the latter approximately 5%. The main influencing factors on the inlet NOx concentration are the nitrogen content in the fuel and the combustion temperature in the furnace. This invention uses LIBS (Liquid Metal-Induced Booster) to identify the N content and a temperature sensing element to obtain the combustion temperature in the furnace.

[0032] Flue gas flow rate is usually measured on-site, but due to the large cross-section of the flue, the measurement results are subject to certain errors. Meanwhile, flue gas flow rate can also be calculated based on fuel composition, and its main influencing variables include:

[0033] Q 烟气 =f(C, H, O, N, S, O2, CO, T, P, RH, Q 燃料 )

[0034] Wherein, C, H, O, N, and S represent the carbon, hydrogen, oxygen, nitrogen, and sulfur elements in the fuel, which can be identified by a LIBS detection instrument. O2 and CO are read from the boiler's dial indicator. T, P, and RH represent the ambient temperature, pressure, and humidity, respectively, obtained through measuring instruments. Q 燃料 The fuel flow rate into the furnace is obtained in real time by the feeding device.

[0035] Obviously, parameters related to ammonia injection rate can be obtained through on-site measuring instruments and LIBS, thereby obtaining the ammonia injection rate feedforward and accurate flue gas flow rate.

[0036] The present invention proposes a feedforward control method for ammonia injection in biomass boilers based on LIBS identification, such as... Figure 1 As shown, it includes the following steps:

[0037] First, a field test was conducted. During the test, the fuel source was changed, and the nitrogen (N) content in the fuel was recorded using a LIBS (Liquid Iron Scale) instrument (placed on the side of the coal conveyor belt). The furnace combustion temperature and inlet NOx concentration were monitored during the test. Based on the N content, furnace combustion temperature, and inlet NOx concentration, a fitted curve C was obtained. NOx,in =f(N) in N, T), are stored in the database for later retrieval, where N in Where N is the nitrogen content and T is the furnace combustion temperature;

[0038] During fuel feeding, the nitrogen (N) content in the fuel is detected online using a LIBS (Liquidity, Air, and Bit) analyzer, and the data is uploaded to the control center in real time. During fuel combustion, the furnace combustion temperature is monitored online using boiler temperature sensors (such as industrial thermometers), and the data is uploaded to the control center in real time. The control center then uses the detected temperature and N content data, combined with a fitted curve C from its database, to... NOx,in =f(N) in ,T), calculate the predicted value of the inlet NOx concentration;

[0039] In addition to detecting the nitrogen (N) content in fuel, the LIBS analyzer also detects the C, H, O, and S content, combining the readings of O2 and CO with those of T, P, RH, and Q. 燃料 The measured value is used to calculate the theoretical flue gas volume Q. 理论烟气 Theoretical flue gas volume Q 理论烟气 This will affect the measured flue gas volume Q 实测烟气 After correction, the calculated flue gas volume Q is obtained. 计算烟气 The calculation formula is:

[0040]

[0041] Through the above steps, this invention obtains the predicted value of the inlet NOx concentration, calculates the flue gas volume, and combines it with the set outlet NOx concentration value. The feedforward correction amount for the ammonia injection quantity can then be calculated according to the following formula, and this correction amount is applied to the ammonia injection system to control the ammonia injection quantity to change in advance, while the original closed-loop control system remains unchanged:

[0042] Q NH3修正量 =Q 计算烟气 ×(CNOx,in,预测 -C NOx,in,实测 )÷46×17÷1000000

[0043] In the formula, Q NH3修正量 To correct the ammonia injection rate, C NOx,in,预测 C is the predicted value of the inlet NOx concentration. NOx,in,实测 This represents the measured value of the NOx concentration at the inlet.

[0044] In this invention, the source of biomass fuel is usually nearby agricultural and forestry waste, such as straw, sawdust, bagasse, rice husks, etc. A biomass plant may change its fuel over the course of several years from design to construction. During normal operation, the type of fuel may change due to seasonal factors, and even the same type of fuel can vary considerably.

[0045] This invention uses a LIBS analyzer to perform elemental analysis on biomass fuel entering the furnace, obtaining the content of C / H / O / N / S elements in the biomass fuel. The analysis is highly accurate and efficient, and can simultaneously analyze multiple elements and detect almost all solid samples.

[0046] Any parts or structures not specifically described in this invention can be made using existing technologies or products, and will not be elaborated upon here.

[0047] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A feedforward control method for ammonia injection quantity in a biomass boiler based on LIBS identification, characterized in that, Includes the following steps: First, a field test was conducted. During the test, the fuel source was changed, the nitrogen content in the fuel was recorded, and the furnace combustion temperature and inlet NOx concentration were monitored. Based on the nitrogen content, furnace combustion temperature and inlet NOx concentration, a fitting curve was obtained and stored in the database for later retrieval. During the fuel feeding process, the nitrogen content in the fuel is detected online and uploaded to the control center in real time; when the fuel is burned in the furnace, the combustion temperature in the furnace is monitored online and uploaded to the control center in real time. Based on the detected temperature and N content data in the fuel, and combined with the fitted curves in the database, the control center calculates the predicted value of the inlet NOx concentration. Obtain the calculated flue gas volume; Obtain the corrected ammonia injection rate and apply it to the ammonia injection system to control the ammonia injection rate to change in advance. The steps to obtain the flue gas volume include: In addition to detecting the nitrogen (N) content in fuel, the LIBS analyzer also detects the C, H, O, and S content, combining the readings of O2 and CO with those of T, P, RH, and Q. 燃料 The measured value is used to calculate the theoretical flue gas volume Q. 理论烟气 Theoretical flue gas volume Q 理论烟气 This will affect the measured flue gas volume After correction, the calculated flue gas volume is obtained. The calculation formula is: 。 2. The method for feedforward control of ammonia injection in a biomass boiler based on LIBS identification according to claim 1, characterized in that, The expression for the fitted curve is: Among them, C NOx,in NOx concentration at the inlet; N in The nitrogen content is denoted by N; T is the furnace combustion temperature.

3. The method for feedforward control of ammonia injection in a biomass boiler based on LIBS identification according to claim 1, characterized in that, The nitrogen content in fuel is detected online using a LIBS testing instrument.

4. The method for feedforward control of ammonia injection in a biomass boiler based on LIBS identification according to claim 1, characterized in that, The formula for calculating the corrected ammonia injection amount is: In the formula, To correct the ammonia injection rate, This is a predicted value for the inlet NOx concentration. The measured value is the inlet NOx concentration.

Images